PostGIS Raster : Extending PostgreSQL for The Support of ... - CoDE

Figure 5.2: Clipping raster effect [17].
ALTER TABLE dummy_rast ADD COLUMN map_rast raster;
UPDATE dummy_rast SET map_rast = ST_MapAlgebraExpr(rast,NULL,
’CASE WHEN rast < 0 THEN rast+10 ELSE NULL END’)
WHERE rid = 1;
Figure 5.3: Algebra operation on rasters [23].
5.6 Convert Rasters to GDAL Format
5.6.1 Raster to TIFF File
The ST_AsTIFF(raster, numberbands, compression) function returns the selected raster bands as a
single TIFF image (byte array). If no band is specified, it will try to use all bands. Where:
– numberbands: an array of bands used to export (max is 3 bands). The order of the bands is
RGB. For example, ARRAY[3,2,1] maps band 3 to Red, band 2 to green and band 1 to blue.
– compression: a compression type such as JPEG90 (or some other percent), LZW, JPEG or
DEFLATE9.
SELECT ST_AsTIFF(rast, ’JPEG90’) As rasttiff
FROM dummy_rast
WHERE rid=1;
5.6.2 Raster to JPEG File
The (ST_AsJPEG(raster, band/numberbands, quality) function returns the selected raster bands as
a single JPEG image (byte array). Where:
– band: a number that specifies a band for single band export.
– numberbands: an array of bands used to export (max is 3 bands). The order of the bands is
RGB. If more than 3 bands are specified, then only the first band is used. If only 3 bands are specified,
then all 3 bands are mapped to RGB. For example, ARRAY[3,2,1] maps band 3 to Red, band 2 to
green and band 1 to blue. If both band and numberbands are specified, band 1 is used by default.
– quality: a number ranged from 0 to 100. Default is 75.
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